In the existing optical transport network architecture, signal exchange is performed in unit of wavelength, and an exchange matrix would be specific to the level of each optical channel (OCh) signal to exchange and filter the wavelengths. The new spectrum planning and management scheme is proposed in the latest version of a G.872 optical transport network architecture, wherein a concept of frequency slot is introduced.
The frequency slot is a concept in the management sense, and does not bring change to the existing transport plane signal. The frequency slot means that one or more OCh signals act as a whole to be exchanged and forwarded, which represents a group of OCh signals and can be implemented by configuring a piece of continuous spectrum on each node. A frequency slot channel is constituted by a cascade of media element frequency slots between two nodes. The frequency slot channel can contain one or more OCh signals and can facilitate network management, and the frequency slot can be exchanged as a single piece of spectrum. Compared to a single wavelength exchange, a transmission distance can be maximized. Each frequency slot channel is an optical media path and can be represented with a central frequency and spectrum width. As shown in FIG. 1, the available spectrum of one optical fiber can be divided into a plurality of frequency slots, and each frequency slot can contain one or more OCh signals.
Modeling from the management point of view, one frequency slot channel can be used to transport one or more OCh signals, the frequency slot channel can be used as a service layer of the OCh signals, while an OCh layer works as a client layer of the frequency slot channel. The established frequency slot channel can work as Forwarding Adjacency of the OCh layer and as a link for the OCh layer, which is used by the OCh layer for path establishment. The established frequency slot channel publishes in the OCh layer the available spectrum within the channel through routing, and a path computation element in the OCh layer establishes an end-to-end path according to the received information of available spectrum.
In a scene of centralized path computation, for example, before establishing a frequency slot channel, a path establishment module in an ingress node sends a Path Computation Request (PCReq) message to a path computation module in the path computation element (PCE) firstly, and requires the latter to compute an end-to-end frequency slot channel with the appropriate spectrum.
In a scene of conventional path establishment, it is required to carry bandwidth information of a label switched path requested to be established in order to establish the label switched path with the corresponding bandwidth resource, wherein the bandwidth information is information of the maximum number of bytes which can be transported per second. But in the process of establishing the frequency slot channel, it needs to consider constraint information of the spectrum resource, that is, the available spectrum information between the highest frequency and the lowest frequency that can be used in the spectrum, or the spectrum width information.
The spectrum width, as a kind of resource constraint information which is different from the bandwidth and needs to be considered, is not defined to be carried through the similar object in the existing Path Computation Element Protocol (PCEP), thus it is not possible to use the existing PCEP protocol assisting in the path computation element to compute a frequency slot channel.